At larger airports it is common to use boarding bridges in order to facilitate the transfer of passengers to and from aircrafts. Normally the boarding bridges are adjustable in height and are telescopically extensible such that passengers may enter or exit the aircraft without being exposed to weather, and without having to enter the docking area or stand where the aircraft is parked.
In order to make it possible to attach the boarding bridge to the aircraft, the aircraft must be guided to a predetermined stop position at the stand. Generally, the pilot is guided by a lead-in line painted on the ground, which ends in a predetermined stopping position. Additionally, since the view of the stand or docking area is limited from within the cockpit of the aircraft, the pilot is normally guided by either personnel on the ground or, as in more recent years, by a visual docking guidance system (VDGS).
A VDGS typically operates by emitting light pulses, e.g. laser pulses, from a location in connection to the stand, e.g. on the terminal building. The light pulses are normally emitted in a direction along the lead-in line, wherein an approaching aircraft following the lead-in line will reflect the light pulses towards a detector. A control unit in the VDGS may then calculate the distance to the aircraft as it approaches the stopping position. Alternatively, a more complex scanning of the volume in the stand area may be performed by directing the light pulses in different directions in the stand area such that different parts of the approaching aircraft reflects the light pulses, wherein not only the distance to the aircraft may be determined, but also the aircraft type may be identified by analyzing the reflections.
Additionally, the VDGS may include a display arranged, e.g. on the terminal building, at a location where it is clearly visible to the pilot, wherein the display may provide guidance, by means of characters and/or symbols, to the pilot while maneuvering the aircraft to the stopping position.
However, the range of the VDGS is limited for a number of reasons. The maximum energy in the light pulses must be limited in order to comply with laser eye safety regulations. As can be understood, the pilot in an approaching aircraft will be directly exposed to the light pulses, which could lead to eye injuries should the light energy be too high. The same applies to personnel working on the ground in the stand area.
Further, the atmospheric conditions in the stand area affect the range of the VDGS. The atmosphere attenuates, absorbs and scatters the light pulses, especially in situations where the weather conditions include fog or heavy rain. Thus, the effective range of a laser equipped VDGS is normally in the range of 100-200 m under ideal conditions.
It is important that an approaching aircraft is detected as early as possible when travelling towards the parking position (at the stopping point). This is especially important from a safety perspective, wherein the approaching aircraft must approach the stand in a manner which minimizes the risk for it coming into contact with objects on the ground as well as the bridge and the terminal building itself. An early detection makes it possible to provide better guidance to the pilot, and also makes it possible for the VDGS to make a better determination of the type and/or version of aircraft that is approaching. The latter is especially important as the boarding bridge must be aligned correctly to the aircraft once it reaches the stopping point.
The operation of the VDGS may roughly be divided into two stages: a capture stage where the VDGS scans the volume in connection to the stand in order to detect/find an aircraft, and a tracking stage where the VDGS has found an object/aircraft and seeks to determine the type and/or version of the aircraft, as well as guiding the aircraft to the stopping point. During the capture stage the VDGS may need to scan over a large volume depending on the layout of the airport and in particular depending on the arrangement of the stands, i.e. some stands may cover large area (normally an area corresponding at least to the size of the largest expected aircraft, e.g. an 80 m by 80 m square), wherein the range of the VDGS must be large in order to reach to the far end of stand. Additionally, the VDGS must be able to scan over a great angle in order to capture objects (aircraft) approaching from the sides.
Attempts have been made to provide early detection of aircrafts by arranging the VDGS further into the stand area, away from the stopping point, such as on a separate post in connection to the entry point of the stand area, or on a portion of the boarding bridge closer to the entry point of the stand area. However, since it is desirable to minimize the number of objects in the stand area both esthetic and safety considerations strongly limit the feasibility of such arrangements.
Accordingly, there exists an unfulfilled need for a system and method for identifying and guiding an aircraft to a stopping position. There furthermore exists an unfulfilled need for such a system and method, which provides reliable operation even under unfavorable environmental conditions such as fog, heavy rain, snow etc., and that reduces the potential for incorrectly identifying the aircraft type to be parked.